Another tool to measuring your brew’s specific gravity is a refractometer.  It can measure the amount of sugar in a liquid by the amount the liquid refracts light.

Fascinating stuff!

Refractometer

To measure your brew’s specific gravity, a small sample (a few drops) are placed on the triangle end of the refractometer. Once the sample has been placed on the tip, the cover is closed down. To take a reading, you take the round end and place it up to your eye. The triangle end is pointed towards a light source which allows the refraction to be captured and presented to the viewer through the eyepiece.

The refractormer measures specific gravity using the Brix scale, which can be converted to other units of measurement like the Balling Scale or Plato degrees.

It’s more expensive than a hydrometer, but it uses a much smaller sample…and it’s 10 times as cool.